Medical Oncologist
CION Cancer Clinics
What an MMR-deficient result means for your family | CION Cancer Clinics
An MMR-deficient result is a finding about the tumour, not a verdict on your family. Most deficient colon cancers come from a gene switched off inside the tumour itself, and relatives are not at raised risk because of it. A smaller group points to Lynch syndrome, an inherited condition that brothers, sisters and children can be tested for. This page explains how doctors tell the two apart and what each answer means. At CION Cancer Clinics in Hyderabad, our oncologists explain colon cancer in plain words and plan care around you and your family.
NG
Medically reviewed by Dr. Naresh GunduConsultant Medical Oncologist · MBBS, DNB (Internal Medicine), DM (Medical Oncology, AIIMS) · last reviewed October 2026, next review due October 2027
17+specialists on panel
15,000+patients treated
35+centres across Telangana & AP
4.8★ / 800+Google rating
The short answer
Does an MMR-deficient tumour mean my family is at risk?
Usually not. MMR stands for mismatch repair, a set of proteins that fix small copying errors in DNA. A deficient result means the tumour has lost one of those proteins. In most people that loss happened inside the tumour alone, and relatives carry no extra risk because of it.
Why the result still gets a second look
In a smaller group, the loss comes from Lynch syndrome, an inherited fault present in every cell from birth. Lynch raises the risk of bowel cancer and, in women, of womb and ovarian cancer. It can pass from a parent to a son or daughter. So a deficient result is never simply filed away. It starts a short chain of further tests on the same tumour tissue, which tells the two situations apart.
Two questions, kept separate
The result answers two questions at once. One is about your own treatment, which our page on what MSI-high status means covers. The other is about your family, and that is what this page is for. Keep the two apart in your mind. A deficient tumour can change your chemotherapy plan without saying anything about your children.
Deficient describes the tumour. Only a blood test can describe you, and only a blood test can describe your relatives.Where the trail leads
Which of three answers is your family likely to get?
Every deficient result ends in one of three places. The one you reach decides whether anybody else in the family needs a test.
A gene switched off in the tumour
This is the most common answer, especially when cancer is found later in life. A gene called MLH1 has been silenced inside the tumour by a chemical tag, a change called methylation. It is not in the blood, so it cannot be inherited.
What it means for family
- No genetic test is needed for relatives
- Screening follows the usual family-history advice
- This result adds nothing to your children's risk
An inherited fault, called Lynch syndrome
A blood test finds a fault in one of the mismatch repair genes, present in every cell since birth. Each brother, sister and child has an even chance of carrying the same fault. Each can be tested for that exact change.
An even chance applies to each person separately. It is a coin toss every time, not a fixed share of the family.Deficient, but unexplained
Sometimes the tumour shows no silencing and the blood test finds no fault. Doctors call this Lynch-like. Often the tumour has damaged both copies of the gene by itself, but that cannot always be proved. Relatives are then advised on the family history and the counsellor's judgement.
How you find out which
Two clues decide the route. One is which protein is missing on the staining. The other is whether the tumour carries a BRAF change or MLH1 silencing. Your pathology report may already hold both answers.
Not sure whether this applies to you?
Ask an oncologistAfter the result
What tests come next, and in what order?
Read which protein is missing
The staining test checks four proteins: MLH1, MSH2, MSH6 and PMS2. Loss of MLH1 together with PMS2 is the pattern most often caused inside the tumour. Loss of MSH2, MSH6 or PMS2 alone points more strongly to an inherited cause.
A second check on the same tissue
When MLH1 is missing, the laboratory looks at the stored tumour sample for a BRAF change or MLH1 methylation. If either is found, the cause almost always started in the tumour. No new biopsy is needed.
Genetic counselling
If the cause is still unexplained, you meet a genetic counsellor. They draw the family tree on both sides, explain what each blood result would mean, and take the questions you would rather ask before the test than after it.
A blood test for you
One blood sample is checked for a fault in the mismatch repair genes in your own cells. The laboratory will tell you roughly when to expect the report, and the counsellor explains it with you.
Testing your relatives
If a fault is found, close relatives can be tested for that one exact change. This is simpler than the first search. A relative who tests negative goes back to the ordinary screening advice for their age.
If Lynch is confirmed
What is offered to each person in the family?
Who
What is usually offered
Brothers and sisters
A blood test for the family fault, and regular colonoscopy for those who carry it
Sons and daughters
The same test, usually once they are adults and can choose for themselves
Parents
Testing can show which side of the family the fault came from
Aunts, uncles and cousins
Offered testing on the side the fault came from, one branch at a time
Women who carry the fault
Advice on womb and ovarian risk as well as the bowel
Anyone who tests negative
Ordinary screening for their age, with no frequent colonoscopy
Leave a number, we will call you
One field. No form to fill in, and no charge for the call.
Did you know
A brother or sister who tests negative for the family's exact fault does not carry a hidden share of it. Their bowel cancer risk is that of the general population, and they can skip the frequent colonoscopies a carrier needs.
Being straight with you
What this page cannot tell you
It cannot tell you which of the three answers your family will get. That depends on the exact proteins lost, the follow-up tumour test and, if needed, your own blood result. Bring the full pathology report to your oncologist rather than reading one line of it online.
It cannot set a screening plan for a relative
Carriers of Lynch syndrome are usually advised colonoscopy every year or two, starting in early adulthood, at an age that depends on the gene involved. Women may also discuss womb and ovarian risk once their family is complete. The exact plan comes from the counsellor and the relative's own doctor. If your result stays unexplained, the page on Lynch-like syndrome explains how families are advised.
Who this does not apply to
If your tumour was MMR proficient, or stable on an MSI test, this page is not about you. Family advice then rests on your family history alone. If a deficient result was explained by methylation or a BRAF change, your relatives need no genetic test because of it.
Deciding who to tell, and how, is hard in a large family. Our guide to telling your family about inherited risk may help.Questions we are asked
Common questions about an MMR-deficient result
Does MMR-deficient mean I have Lynch syndrome?
No. It means the tumour has lost a repair protein. Most deficient colon cancers are caused by a gene switched off inside the tumour, which cannot be inherited. Only follow-up tests on the tumour, and sometimes a blood test, can show whether Lynch syndrome is behind it.
My report says MLH1 and PMS2 are lost. Should my children worry?
Not yet. This pattern is the one most often caused by silencing inside the tumour. Ask whether BRAF or MLH1 methylation testing has been done on the same tissue. If either is positive, the cause is almost always not inherited and your children need no genetic test because of it.
Who in the family should be tested first?
The person who has the cancer, whenever possible. Their blood test shows whether there is a family fault to look for at all. If none is found, testing healthy relatives usually adds nothing, and their advice is based on the family history instead.
What if the relative with cancer has already died?
Stored tissue from their old surgery or biopsy can sometimes still be tested at the hospital that kept it. If that is not possible, a genetic counsellor can decide whether testing a living relative directly makes sense, based on the family tree and the old reports you can find.
Should my children be tested now?
Usually not while they are children. Bowel checks for Lynch syndrome do not start in childhood, so testing normally waits until they are adults and can decide for themselves. A counsellor can help you plan how and when to explain it to them.
Does a deficient result change my own treatment?
It can, and that is a separate question from your family. It may affect whether chemotherapy after surgery helps, and in advanced disease it can open the door to immunotherapy. Your oncologist and the tumour board weigh this for your stage.
Will a carrier result affect a son's or daughter's marriage?
A genetic result is private health information. Who is told, and when, is the family's decision. Many families worry about this quietly. A counsellor will talk it through honestly, including how carriers who are watched closely tend to have problems found early.
Where do I start in Hyderabad?
Take the full pathology report to your oncologist and ask what follow-up tumour tests have been done. CION's oncologists can explain the report, discuss it at the tumour board and arrange a genetic referral if it is needed. Call the helpline if you are unsure who to ask.
Your Specialists
Meet CION's colon cancer specialists. Bring your colonoscopy, scan or biopsy report.
Our surgical and medical oncologists plan colon cancer care together: which operation, whether chemotherapy is needed, and the follow-up that comes after.
Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
Medical Oncologist
Medical Oncologist
Surgical Oncologist
Dr. Muralidhar Muddusetty
MBBS (AIIMS), MS (Surgery) (AIIMS), DNB (Surgical Oncology), MRCS (Edinburgh)
Surgical Oncologist
Want a specific doctor for your case? Mention them when booking.
Book Free ConsultationBook an appointment with our specialist
Share your name and number — we'll call you back within 30 minutes to schedule your consultation.
Sources
- NICE — Molecular testing strategies for Lynch syndrome in people with colorectal cancer
- National Cancer Institute — Genetic Testing Fact Sheet
- American Cancer Society — Colorectal Cancer Risk Factors
- Cancer Research UK — Risks and causes of bowel cancer
This page is general information, not a prescription. Do not change or stop any treatment based on what you read here. If anything is worrying you, contact your own treating team — or call our helpline and we will help you reach the right specialist.
Keep reading
Related pages
Lynch syndrome and colon cancerThe inherited condition a deficient result may point toGenetic testing after a colon cancer diagnosisHow the blood test is arranged and what it looks forScreening for siblings and parentsWhat brothers, sisters and parents should do nextUniversal MMR and MSI testingWhy every colon cancer is tested in the first place
Talk to us
Holding an MMR-deficient report and unsure what to tell the family?
Share the pathology report and we will explain which follow-up tests have been done, which have not, and whether a genetic referral makes sense for you. One helpline serves every CION centre.